Strongly resembling or composed largely of gneiss; showing marked gneissic characteristics.
From gneiss plus -itic suffix, an intensified form of -ic. The -itic suffix (seen in granitic, basaltic) emphasizes the characteristic quality, suggesting 'rich in' or 'dominated by' the mineral.
The difference between gneissic and gneissitic is subtle but useful—gneissitic means something is really, truly gneiss-like, showing geologists value precision even when describing rock types!
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